Sub-size Specimens Research Articles

Optimum use of broken Charpy specimens from surveillance programs for the application of the master curve approach

Broken Charpy specimens can be used in various ways to determine the reference temperature, T 0, as defined in the Master Curve approach. Reconstitution and machining of subsize specimens are two solutions for direct toughness evaluation. The optimum technique and specimen geometry preferentially: use a minimum number of broken half Charpy’s, have a small uncertainty on the reference temperature, have the widest valid test temperature window, have a reasonable cost, and are easy to perform into hot cells. In this study, the use of various miniature specimen types such as Compact (C(T)), Single Edge notch Bend, (SE(B)), or Miniature Precracked Charpy (MPCCv), and Circumferentially Cracked Round Bars (CRB), is investigated. As this study deals with small specimens, the problem of loss of constraint is also addressed. Taking all constraints into account, a 0.16T−C(T) specimen is found to be the more promising geometry. This work is supported by experimental data generated on various specimen types and sizes on the well-characterised reactor pressure vessel steels 22NiMoCr37, 20MoNiCr55 and JRQ.

Upper shelf energy normalisation for sub-sized Charpy-V specimens

When the plate thickness is less than 10 mm, testing with standard sized Charpy-V notch specimens is impossible. In such cases the testing must be based on sub-sized specimens. Sometimes, standard size specimens are impractical also for thicker sections. The use of sub-sized specimens requires extrapolation of the result from the sub-sized specimen to correspond to the result from a standard sized specimen. In this work, literature data combined with newly generated data were collected and examined in order to find the correct normalisation procedure for sub-sized specimen, upper shelf impact energy data. The resulting normalisation procedure, combined with a new Charpy-V-J–R curve correlation, was shown to produce realistic estimates of the materials upper shelf fracture toughness. In the case of materials showing pronounced splitting in the Charpy-V test, the estimates may be over-conservative.

Embrittlement behaviour of different international low activation alloys after neutron irradiation

The embrittlement behaviour of ferritic/martensitic steels after irradiation in the Petten high flux reactor (HFR) was investigated by instrumented Charpy-V tests with subsize specimens. The main objective, apart from studying effects of particularly low doses, was a comparison of low activation alloys (LAA) from various countries with different Cr contents and different types and concentrations of minor alloying elements and impurities. In the present report, the results of another three materials (OPTIMAR, OPTIFER-IV, GA3X) obtained within the second phase of the MANITU programme (0.8 dpa, at 250–450°C) were analysed and assessed in comparison to the results of the first irradiation up to 0.8 dpa. The evaluation clearly showed a reduced embrittlement problem for the advanced reduced-activation alloys. Of the examined alloys, the GA3X steel shows the very best embrittlement behaviour after neutron irradiation.

Material Damage Evaluation of Primary Power Plant Components Using Sub-Size Specimens

Material Damage Evaluation of Primary Power Plant Components Using Sub-Size Specimens

Material Damage Evaluation of Primary Power Plant Components Using Sub-Size Specimens

This paper addresses several experimental techniques that have been developed and validated with the aim of assessing the mechanical conditions of service-exposed primary plant components, particularly from the point of view of fracture toughness. Such techniques are based on the use of specimens of small or even miniaturized size, as an alternative to the “conventional” methodologies described by commonly used test standards.

Mechanical Characterization of Two Low-Activation Chromium Alloys in As-Received and Heat-Treated Conditions

In recent years, within the fusion long-term programmes, attention has been devoted to the characterization of Chromium (Cr) alloys, in view of their elevated corrosion resistance, low activation properties and high-temperature mechanical strength.As part of the European Fusion Programme, an activity has been launched in 1999 with the aim of exploring the potential of Cr alloys as structural materials in fusion reactors, for example, as first wall or blanket materials. Recent investigations have focused attention on two commercially available materials: high-purity 99.7% Cr (DUCROPUR) and Cr alloyed with 5% Fe and 1%Y203 (DUCROLLOY), both of which have shown excellent low activation characteristics.The mechanical properties of these two alloys, in both as-received and heat-treated conditions, have been characterized at SCK•CEN by means of tensile, instrumented impact and static three-point bend tests, using standard and sub-size specimens. Tensile tests have also been carried out on samples irradiated at 300 °C in the BR2 reactor in Mol up to an accumulated dose of about 0.5 dpa.

Charpy-V Subsize Specimens

Subsize specimens in Charpy impact tests has are a valuable substitute to predict the ductile-to-brittle transition temperature (DBTT) and the upper shelf energy (USE) anticipated for full size specimens where volume limitations exist. The subsize specimens have been applied to testing of several steels and the data has been compared to those of standard full size specimens. The common normalization on the basis of fracture area does not produce any correspondence between the two different sized specimens therby showing an apparent decrease in both USE and DBTT by using subsize specimens.

Towards standardising a sub-size specimen for fatigue crack propagation behaviour of a nuclear pressure vessel steel

Constant load amplitude fatigue crack growth rate (FCGR) behaviour of A533B steel was studied using compact tension (CT) and three point bend (TPB) specimens. TPB specimens belonged to two categories, namely, span to width ( S/ W) ratio equal to 4 and 2 respectively. The thickness of TPB specimens was 10 mm while CT specimens were of 10 and 20 mm thickness. Paris law constants were obtained for the different geometries of CT and TPB specimens. It has been confirmed that size effects are absent for the test conditions investigated. During the fatigue testing of TPB specimens, unloading compliance was determined using a crack mouth opening displacement (CMOD) gauge fitted at the level of the notch mouth. An expression was derived to calculate the crack length in S/ W=2 type of TPB specimens using the unloading compliance values.

Load-carrying capacity and crack resistance of a cladding by the Sigma-oscillating wire technique

If cracks are postulated in the ferritic base material beneath the austenitic cladding, their initiation and propagation under hypothetical loading cases is influenced by the load carrying capacity of the cladding. The toughness of the KKS-RPV cladding was assessed by means of elastic-plastic fracture mechanics methods. Sub-sized tensile and bend specimens were fabricated by reconstitution technique from broken halves of standard ISO-V Charpy specimens, representing crack extension in radial and circumferential direction. They were tested and evaluated and further analyzed with the Gurson model. For temperatures relevant to the loss of coolant and upset conditions analyzed, a sufficient toughness of the cladding in terms of J and CTOD resistance curves could be shown.

Embrittlement behaviour of different international low activation alloys after neutron irradiation

The embrittlement behaviour of ferritic/martensitic steels, after irradiation in the Petten High Flux Reactor (HFR), was investigated by Charpy-V tests with subsize specimens. The main objective, apart from studying the effects of particularly low doses, was to compare the irradiation response of low activation alloys from various countries with different levels of Cr, minor alloying elements and impurities. Specimens were irradiated at temperatures ranging between 250°C and 450°C to dose levels between 0.2 and 2.4 dpa. The evaluation clearly showed a tendency to a much reduced embrittlement problem for the advanced reduced-activation alloys; it could not, however, be attributed to lower Cr-contents. Instead, the role of helium, already suspected in our earlier work, could be correlated with the characteristic burn-up of different boron levels in the steels. This correlation translates for a fusion reactor environment into a non-saturating deterioration of alloys even without any boron, due to helium-yielding high energy neutron reactions with the base elements. Though the effect seems to be less detrimental for the more homogeneous distribution of the helium in the matrix.

Integrated technologies for life assessment of primary power plant components

Assessing the integrity and stability of high-temperature, service-exposed components is increasingly a topic of interest for power plant users. The present paper describes various approaches developed by ENEL and CISE for the life assessment of such components. Alternative test techniques, mainly based on sub-sized specimens, have been developed and validated for deriving reliable information from small quantities of sample material, as well as empirical correlations based on `conventional' test data. A particular case is discussed, highlighting the risk of non-conservative flaw assessments under conditions of fatigue with negative peak loads.

Standards for Fracture Toughness Testing of Rock and Manufactured Ceramics: What Can We Learn for Concrete?

AbstractThis paper presents a review of the American Society for Testing and Materials (ASTM) and the International Society for Rock Mechanics (ISRM) standards for determining the plane-strain fracture toughness of cemented carbides and rocks, respectively, with an eye toward applicability to concrete. The evolution of the chevron-notched test specimen used in these standards is briefly reviewed. A discussion of a particular chevron-notched configuration, the short rod test specimen, and associated test methods follows. The ASTM and ISRM standards are then described. The paper evaluates the potential for learning from, modifying, or adapting these standards for use on a standard fracture toughness test for concrete. The potential advantages and disadvantages of using the short rod geometry and testing methods on concrete are discussed, taking into account fracture response, shape, volume, preparation, precracking, symmetry, and subsize specimen effects. Preliminary research into the applicability of the short rod geometry and testing procedures on concrete is discussed.

Effect of ageing and specimen size on the impact properties of MANET II steel

Abstract In the present work, the effect of ageing at 550°C for 1000 h on the impact properties of MANET II steel was investigated. Two different Charpy V-notch impact specimens were used: full-size and sub-size specimens. Tests were carried out on two instrumented impact machines appropriate for the two specimen size. Both microstructure and fracture surface were examined using optical and scanning electron microscopy (SEM). The results showed that ageing produced little embrittling effect on MANET II steel. Both the duetile-to-brittle transition temperature (DBTT) and the brittleness transition temperature ( T D ) were increased by about 15°C. The local fracture stress was also slightly reduced due to the ageing treatment. The results were discussed in the light of the chemical composition and the fracture surface morphology.

Effect of lay-up sequence on mechanical properties and fracture behaviour of advanced CFRP laminate composite

Long carbon fibers with 5.5 GPa in average tensile strength-reinforced epoxy plastic laminates (CFRP) have been studied to determine the effect of the lay-up sequence on the mechanical properties and fracture behavior of the advanced CFRP composite. The mechanical properties were evaluated by three-point slow bend and instrumented Charpy impact tests. Two mm-V notch subsize specimens with angles of 0, 45 and 90 ° between the fibers of the 0 ° layers and longitudinal direction of the specimen ((0 °), (45 °) and (90 °) specimens) were used. The unidirectional laminate (0 °/0 ° ply-(0 °)) specimen exhibited high slow bend and Charpy impact energies, but the 0 °/0 ° plies had a remarkable anisotropy of the mechanical properties. The mechanical properties of the orthotropic laminates (0 °/90 ° plies-(0 °) and (90 °)) specimens significantly decreased but those of the 0 °/90 ° ply-(45 °) specimen dramatically increased. There was a marked benefit in the mechanical isotropy for quasi-isotropic laminates (0 °/90 °/ ±45 ° plies). However, slow bend and Charpy impact energies of the 0 °/90 °/ ±45 ° plies-(0 °), (45 °) and (90 °) specimens were 60 and 70%, respectively, of those of the 0 °/0 ° ply-(0 °) specimen. The results are described and discussed.

The Effect of Specimen Size in Charpy Impact Testing

Charpy V-notch impact tests were performed on the full-, half-and third-size specimens from two ferritic SA 508 Cl. 3 steels for nuclear pressure vessel. New normalization factors were proposed to predict the upper shelf energy(USE) and the ductile-brittle transition temperature(DBTT) of full-size specimens from the measured data on sub-size specimens. The factors for the USE and the DBTT are respectively, where B the width, b the ligament size, the elastic stress concentration factor, and R the notch root radius. These correlations successfully estimated the USE and DBTT of the full-size specimens based on sub-size specimen data. In addition, the size effects were studied to develop the correlations among absorbed energy, lateral expansion(LE) and displacement. It was also found that the LE was able to be estimated from the displacement obtained by the instrumented impact test, and that the displacement would be used as a criterion for the toughness of the steels corresponding to change in their yield strength.h.

Low temperature embrittlement behaviour of different ferritic-martensitic alloys for fusion applications

In the last few years a lot of different low activation CrWVTa steels have been developed world-wide. Without irradiation some of these alloys show clearly a better low temperature embrittlement behaviour than commercial CrNiMoV(Nb) alloys. Within the MANITU project a study was carried out to compare, prior to the irradiation program, the embrittlement behaviour of different alloys in the unirradiated condition performing instrumented Charpy impact bending tests with sub-size specimens. The low activation materials (LAM) considered were different OPTIFER alloys (Forschungszentrum Karlsruhe), F82H (JAERI), 9Cr2WVTa (ORNL), and GA3X (PNL). The modified commercial 10–11% CrNiMoVNb steels were MANET and OPTIMAR. A meaningful comparison between these alloys could be drawn, since the specimens of all materials were manufactured and tested under the same conditions.

Fatigue behavior of copper and selected copper alloys for high heat flux applications

The room temperature fatigue behavior of standard and subsize specimens was examined for five copper alloys: OFHC Cu, two CuNiBe alloys, a CuCrZr alloy, and a CuAl 2O 3 alloy. Fatigue tests were run in strain control to failure. In addition to establishing failure lives, the stress amplitudes were monitored as a function of numbers of accrued cycles. The results indicate that the alloys with high initial yield strengths provide the best fatigue response over the range of failure lives examined in the present study: N f = 10 3 to 10 6. In fact, the fatigue performance of the best alloys is dominated by the elastic portion of the strain range, as would be expected from the correlation of performance with yield properties. The alumina strengthened alloy and the two CuNiBe alloys show the best overall performance of the group examined here. The fatigue response was found to be closely related to the uniformity of the material microstructure and particularly the distribution of the finely dispersed strengthening phases. The pre- and post-fatigue microstructures were examined to identify the types and distribution of secondary phases, and their role in fatigue response.

Charpy impact properties of low activation alloys for fusion applications after neutron irradiation

The MANITU irradiation and fracture-toughness testing program although initially foreseen to clarify the early dose-saturation of ΔDBTT for commercial ferritic steels has been extended to include the medium temperature (≥ 250°C) irradiation hardening behaviour of promising low-activation alloys. The results after a first 0.8 dpa irradiation clearly show a much better behaviour of the new alloys in any respect (e.g. DBTT after irradiation always below +50°C for subsize specimens, for the ORNL steel even below −20°C). The complexity of temperature dependency is probably caused by the transition range in dose accumulation, and should therefore not be ‘over-interpreted’.

Investigation of samples taken from Kozloduy unit 2 reactor pressure vessel

Within the framework of the 6 month WANO program, small samples were cut from the inside surface of the Kozloduy NPP unit 2 reactor pressure vessel to assess the actual condition of the pressure vessel material before and after annealing. The actual values of the weld metal characteristics required for estimating radiation-limited lifetime—the ductile-to-brittle transition temperature (DBTT) in the initial state ( T ko) and the phosphorus and copper contents which affect the radiation stability of steel—were not determined during manufacturing. The Kozloduy unit 2 pressure vessel had no surveillance program. Radiation stability was evaluated using dependencies based on analysis results for surveillance samples taken from other VVER-440 reactors. For this reason, the actual pressure vessel characteristics and their changes in the course of reactor operation, as well as comparison of experimental with calculated data were the principle objectives of the study. Instrumented impact tests were carried out on sub-size specimens of base and weld metal. Correlation dependencies were used with standard tests to determine DBTTs for the base and weld metal (in accordance with Russian standards): base metal before annealing 40 °C, after annealing 16 °C; weld metal before annealing 212 °C, after annealing 70 °C. The estimated value of T ko, for the initial, unirradiated weld metal, was 50 °C. The experimental results were compared with a prediction of the extent of radiation-induced embrittlement of Kozloduy unit 2 pressure vessel materials. It was confirmed that radiation-induced embrittlement of the base metal does not impose any limits on the radiation-limited lifetime of the pressure vessel. The predicted increase in the DBTT of the weld metal as a result of irradiation (about 165 °C) is practically equal to the experimental result (162 °C). However, the value of T f obtained from tests before annealing (212 °C) is about 40 °C higher that the estimated value, i.e. the calculation does not produce a conservative estimate. This was explained by a low estimate of T ko (10 °C), which had been calculated using data from chemical analysis of the weld metal, performed by the manufacturer. The investigations on the samples, however, yielded an estimated value of T ko = 50 °C. The effectiveness of annealing in restoring the mechanical properties of irradiated VVER-440 reactor pressure vessels was confirmed. Recovery annealing lowered the DBTT of the weld metal by 85% or more of its radiation-induced shift.

Size effects on the upper shelf energy of a neutron irradiated pressure vessel weld metal

The methodologies published earlier for predicting the upper shelf energy (USE) of full size Charpy specimens based on subsize test data appear to work satisfactorily for either highly materials (USE > 200 J) or relatively brittle materials (USE ≪ 100 J). A methodology is proposed here that works well for pressure vessel weld materials in both unirradiated and irradiated conditions having USE in the intermediate region (100 J < USE < 200 J). The methodology uses partitioning of the USE into two components, USE p and δUSE ( = USE - USE p). USE p is the absorbed energy for a specimen fatigue-precracked to half the width. The predicted value of the USE of full-size specimens is a sum of two terms. The first term is equal to product of the normalized δUSE of the subsize specimen and the full-size normalization factor for δUSE. The second term is equal to the product of the normalized USE p of the subsize specimen and the fracture volume of the full-size precracked specimen. The predicted values were within about 10% of the measured values for both unirradiated and irradiated materials.